In the chemical or pharmaceutical industry it is often important to conduct analyses of substances in a fluid with a small sample quantity and a high throughput.
DE 10308975B4 discloses a piezoelectric resonator whose resonant frequency changes when a fluid containing substances is applied to the surface of the resonator, said substances being adsorbed by the resonator surface. The technology employed to build the resonator is also referred to as “film bulk acoustic wave resonator” (FBAR). The substance present in the fluid is absorbed by the chemically sensitive surface of the resonator. The concentration of the substance in the fluid can be determined by measuring the change in resonant frequency. In most cases it is merely desired to ascertain one parameter, such as the mass binding of the substance, as a result of which the concentration of the substance in the fluid can also be deduced.
The other parameters which can influence the resonant frequency are interference effects. For example, the resonator frequency changes for example as a function of the temperature, mechanical stress or vibration. In certain conventional systems these undesirable effects must be kept constant during the measurement. This may be achieved for instance by means of a heating system which keeps the sensor/acoustic resonator at a constant temperature. In addition the measurement setup may be mounted on a stable base in order to avoid forms of interference caused by vibrations.
One possibility of reading out temperature and mass binding simultaneously or of measuring the same with the aid of the acoustic resonator is to measure the temperature separately from the resonator, with a platinum resistor for instance. This method is often inaccurate due to the measuring imprecision and inertia of the sensor.